444 ELEMENTS OF BIOLOGY 



structure, the cnidocil, which when stimulated causes a discharge of 

 the nematocyst. 



CcELOM. The body cavity of Metazoa. The cavity formed between the 

 inner and outer sheets of mesoderm in the embryo. 



CcELOMATE. The ccelomate animals are those that have a ccelom, for ex- 

 ample, the vertebrates. 



Cohesion. The attraction for each other exerted by like molecules. 



Colloid. A combination of two or more substances in which one or 

 more are divided into particles greater than one molecule and 

 suspended in another substance. 



CoMMENSALisM. Two orgauisms intimately associated in such fashion 

 that both obtain food from the same source. 



Complementary genes. See AUelomorphic genes. 



Complete metamorphosis. Describes insects which pass through four 

 stages in their life history — eggs, larva, pupa and adult. 



Conditioned reflex. A response which by repetition has been con- 

 verted from a conscious act into a reflex. 



CoNjuGANT. Used to refer to a member of an associating pair in the 

 process of interchange of micronuclear materials between Protozoa. 



Contractility. The property of changing shape as shown by living 

 organisms. 



Corium. See Dermis. 



Correlation. The unification of parts in the cell or In the organism to 

 accomplish the life processes of the whole. 



Cretin. A type of mentally and physically defective person. The defects 

 are due to malfunction of the thyroid gland. 



Cyclosis. The constant streaming of protoplasm within the cell; com- 

 monly observed in various Protozoa. 



Cysticercus. a stage in the life history of the tapeworm in which the 

 animal has the foriTi of a bladder containing the inverted head; it 

 develops in the muscles of swine. 



Cytology. The science which treats of the minute structure of the cell. 



Cytoplasm. Protoplasm outside the cell nucleus, exclusive of the proto- 

 plasm that forms the plasma membrane of the cell. 



Defecation. The expulsion of undigested and indigestible material. 



Dendrite. The elongated portion of the nerve cell, which conducts im- 

 pulses toward the cell body. 



De-nitrifying bacteria. Soil bacteria that in their metabolism liberate 

 gaseous nitrogen from its soil compounds into the air. 



